Day1-python Basics 1 Introduction, basic syntax, Process Control

Day1-python Basics 1 Introduction, basic syntax, Process Control

　　1.Python Introduction

　　Note: Programming languages are mainly categorized from these angles, compiled vs explanatory, dynamic vs static, and strongly defined vs weakly defined type languages

　　　1.1.Python is a dynamically explanatory strong-type definition language

Dynamic type language: a language that checks data types when executing a program, does not specify a data type when programmed, and the first time the program runs

When assigning a value to a variable, the data type is recorded inside the program

Static type language: Check the data type at compile time, and declare the data type of all variables when programming

Explanatory type: Only when the program is executed, one article is interpreted into machine language execution, operating efficiency is low, such as Python/ruby

Compiled: Each statement of the source program is compiled into a machine language, and saved as a binary file, run quickly, such as C + +

Strongly typed definition language: Refers to a language that enforces the definition of a data type, unless the variable data type is coerced, the data type never

Change, is a type-safe language

Weak type definition language: A variable can assign values of different data types

Advantages and disadvantages of 1.2.Python

Advantages: 1. High-level language, simple and easy to learn; 2. Code portability is strong, support multi-platform; 3. Rich third-party library development efficiency

Cons: 1. Slow operation, 2. code cannot be encrypted; 3. Multithreading is not supported

1.3. Interpreter

The installed Python comes with the official interpreter CPython, which is the most widely used interpreter

. PYC is a file that is generated when Python executes

　　2. Basic syntax

2.1. Variables

Constitute:

• • Variable names can only be combinations of letters, numbers, and underscores
  • Cannot use special characters and cannot start with a number
  • Keyword cannot be declared as a variable name

How to write:

• • the name of the "my_name" variable is meaningful, and it is recommended for Python to use an underscore connection.
  • "MyName" hump type, C + + and other general use this way

2.2. Character encoding and Binary

Character encoding: ASCII (early, English only)--->gb2312 (supports 7K multi-kanji)--->gbk18030 (supports 20K multi-kanji)--->GBK (supports 70K multi-kanji)--->unicode (Universal code, Support for all national characters)

UTF-8: Variable long version Unicode, space-saving, character-occupying space between 1~4 bytes

2.3. User interaction Mode

Python2.x:raw_input ("Please enter:")----->python3.x:input ("Please Enter:")

　3.for Cycle

　　　Iterate through all the elements of a sequence, including lists, strings, etc.　　

#-*-coding:utf-8-*-ImportSYS#1. Traversing a string forLetterinch 'Hello':    Print("Letter :", letter)#2. Iterating through the list elements through an indexFruits = ['Apple','Banana','Mango'] forIndexinchrange (len (fruits)):Print("Current Fruit:", Fruits[index])#3.for....else Statements#The Else statement executes after the for normal execution is complete, that is, the for is not broken out by break forIinchRange (3):    Print(i)Else:    Print("For loop normal end display") forIinchRange (3):    Print(i) Break        #For loop Abnormal endElse:    Print("For loop normal end display")#will not be executed

4.while Cycle

　　Used to loop the execution of a program, repeating the same task when a certain condition is met

#-*-coding:utf-8-*-#Simple Statement GroupFlag = 1 while(flag):Print('good!')#Normal CycleCount =0 while(Count < 10):    Print("the current values are:", Count) Count+=1Print(">10 Cycle End")#Infinite Loopsvar = 1 while(var = = 1): Num= Input ("haha, come in will not go out:")    Print("What you have entered is:", num)#While....else Cycle#executes when a while loop statement is FalseCount = 1 whileCount < 5:    Print("%s is less than 5, continue"%count) Count+=1Else:    Print("More than 5, can't go on, gameover! .")

5.break and Contiune

Break: Jump out of the loop Contiune: Jump out of the loop

#Contiune: Jump out of this cycle forIinchRange (10): I+=1ifi = = 5:        Continue       #Print all except 5    Print(i) Count=0 while(Count <10): Count+=1ifCount = = 5:        Continue       #Print all except 5    Print(count)#Break : Jump out of this cycle forIinchRange (10): I+=1ifi = = 5:         Break       #5 End after not printing    Print(i) Count=0 while(Count <10): Count+=1ifCount = = 5:               Break       #5 End after not printing    Print(count)

6. Table-Over if: Elif. Else statement

else: executed when the IF statement is 0 or false is optional, but an if can only correspond to an else

Elif: Allows you to check if multiple results are true, and when True, the corresponding code block is executed, elif is optional, but can be any

Day1-python Basics 1 Introduction, basic syntax, Process Control